A DC-DC converter is an electronic circuit that converts a source of direct current from one voltage level to another. DC-DC converters are widely used in portable electronic devices to provide power from a battery as well as following stages to an AC-DC converter, and are used generally in electronic circuits to regulate an output voltage. For example, a DC-DC converter may be used to compensate for varying load current and/or variations in the input voltage.
Measuring current in a DC-DC converter is useful and necessary for a wide variety of control and safety purposes, and it is desirable to do so inexpensively with minimal power loss. However, such measurements can be difficult or require additional components, particularly in switched power converters.
For example, an isolated switched converter, such as an LLC series-resonant converter, has an input powered from a high-voltage DC source. The circuit includes a half-bridge power stage which is connected to the series elements of an LLC resonant circuit. The LLC resonant circuit is formed by a series combination of a magnetizing inductance and a transformer, and a combined capacitance on the output side of the bridge.
A typical solution for sensing the current adds a DC resistor in the primary circuit and senses the voltage drop over the resistor. While this solution is inexpensive, it also creates additional loss and reduces the overall efficiency of the power converter. Another solution is to incorporate a Hall Effect sensor. A Hall Effect sensor is a transducer that senses the magnetic field generated by a current-carrying conductor and generates an output signal (voltage or current) in response to the magnetic field. However, this solution is expensive and complex. An additional solution utilizes a capacitor connected to a capacitive node, but provides limited bandwidth and accuracy.
Thus, it would be desirable to develop an effective alternative solution for accurately sensing current that is inexpensive, does not result in significant power loss, and has a low component count.